This application claims the priority of German Application No. 19904909.2, filed Feb. 6, 1999, the disclosures of which are expressly incorporated by reference herein.
The invention relates to a method for providing traffic information to a given vehicle in a road network as well as a device suitable for working such a method.
Traffic information methods and devices provide road vehicles with information that characterizes the traffic situation to be used for guidance, route selection, travel time estimation, etc. Depending on whether the processing of the traffic information takes place primarily aboard the vehicle or at a traffic center, a distinction is made between autonomous systems and center-based systems. Another distinction is between dynamic guidance systems and static guidance systems. In dynamic systems traffic situation data is taken into account when calculating the optimum route.
In center-based dynamic guidance systems, optimum routes are calculated in a traffic center and relevant data are transmitted to the vehicle. The term "optimum" is used herein to refer to a route for which a cost function, which serves as the basis for an optimization procedure, assumes an optimum value, e.g. a minimum, with the travel time frequently being used as a cost function. A special algorithm for calculating the fastest routes in a road network is described in the journal article by E. W. Dijkstra, "A note on Two Problems in Connection with Graphs," Numer. Math. 1, page 269. Alternatively, however, another cost function can be used. For example, energy consumption required to travel a given section of road referred to herein below as "route path" or "path" for short, can be used as a cost function. In autonomous dynamic guidance systems, the optimum route is calculated aboard the vehicle on the basis of current traffic information transmitted from a traffic center to the vehicle, for example in the form of conventional TMC traffic reports.
Most known dynamic guidance systems are limited to providing and examining current traffic information, i.e. information on the current traffic situation on the road network as obtained especially by traffic situation detectors distributed over the road network. However, the traffic situation, especially conditions relative to traffic flow such as traffic jams and the like (and hence the optimum route between two points in the road network), can change dramatically in a very short time. This can result in drastic deviations in the value of the cost function for an actual trip, such as the travel time or the energy consumption of the vehicle, from the estimated cost function value associated with the optimum calculated route.
Known traffic situation forecasts take the forecast traffic data in addition to the current traffic data, into account for vehicle guidance, route determination, and/or travel time estimation; see for example German Patent Documents DE 195 26 148 C2, DE 196 47 127 A1, and DE 198 06 197 A1, as well as the previously unpublished older German Patent Application 198 35 979.9.
Traffic forecasting methods of this kind are performed at a traffic center because of the associated computing required to be able to provide the forecast traffic data in addition to the current data to participating vehicles. The volume of data here poses a problem since traffic information, because of the limited capacity of the available communications channels, can be transmitted only in very limited quantities from the center to an individual vehicle. Additionally, it is frequently not known precisely at the center, which traffic information is required by a guidance system aboard a vehicle to calculate traffic-dependent optimum routes with a route-searching algorithm available aboard the vehicle. Therefore, there is a need for methods and devices by which reliable traffic information that can be readily evaluated by the vehicle can be provided in the smallest possible quantity of transmitted data, taking into account both current data and timely forecast data forecast about the anticipated traffic situation for the relevant stretches of road.
In German Patent Document DE 198 06 197 A1, methods and devices are described in which current and forecast traffic data are transmitted from a traffic center, organized in accordance with so-called target areas, and transmitted over a corresponding communication channel to the vehicle. To create the target areas, sequential forecast times are determined starting at a starting time and a road network partial area is assigned as a target area area in which the vehicle is expected to be situated during the time, between the forecast time in question and the next forecast time. To determine the target areas, it is proposed to use the anticipated distance of the vehicle from the starting location, as obtained at the time in question, from stored speed data on the average assumed vehicle speed in the road network in question, which can be specified as fixed or a function of the type of road.
The present invention provides a method and a device whereby, at relatively low expense, comparatively reliable and accurate traffic information can be provided for further use by a vehicle on a given road network, especially by an autonomous dynamic guidance system present aboard the vehicle for guidance, route planning, etc.
Traffic information provided by the method and device of the present invention includes a determination, performed by the traffic center, and beginning at a given starting location and starting time, of routes that are optimum relative to a specified traffic-dependent cost function such as travel time, to the route paths of at least one road network partial area containing the starting location. The route-search method operates as a function of traffic data taking into account traffic data that are in the traffic center, current, and forecast, which includes the current and forecast functional values of the cost function for the individual route paths of the road network as well as additional data, depending on the application, on the current and future traffic situation.
The current traffic condition data, as well as at various specified forecast times, for the route paths under consideration are stored at the traffic center, so that they can be called up or can be provided at any time by a conventional traffic forecasting method. The corresponding previously-estimated arrival time, at which a vehicle that starts at the starting location at a starting time and travels the optimum route, can be expected to reach the route edge in question results directly from the optimum route calculated for the individual route path.
The cost function value, which is associated with the arrival time by the optimum route is chosen from the current and forecast values of the cost function for each route path, i.e. the values that can be expected at the specified forecast times. In addition to the selected cost function value, additional traffic data, which are stored at the traffic center for the given route path and the given arrival time can, be selected, as needed. According to the invention, the cost function values for the individual route paths of the road network partial area under consideration are selected in a timely fashion and in accordance with the calculated optimum routes. The partial areas are processed in the center as traffic data that can be transmitted, or in any case constitute a part of the traffic data prepared for transmission.
With this procedure, relatively reliable current and forecast traffic situation data can be produced as compactly as possible, when taking transmission capacity into account. In particular, a guidance system aboard the vehicle with a conventional design without any structural changes is able, with such transmitted traffic information, to perform optimum guidance or route planning which not only employs the current traffic situation but also takes into account the anticipated future traffic situation, because the future traffic situation is provided to the system through the transmitted cost function values for the relevant route paths. In addition, improved accuracy, for such autonomous guidance processes using the traffic information provided according to the invention, is achieved by comparison with conventional systems in which the transmitted traffic information contains course information about any anticipated traffic state objects, such as traffic jams, slow traffic, etc. in a large area at a later forecast time without requiring the transmission of larger amounts of data. In addition, the accuracy with which the cost function values is chosen when compared with the accuracy with which any kind of target areas are conventionally determined (i.e. distance zones around the respective starting location) is increased and no distinction is made in traffic information by such target areas or distance zones.
In a particular embodiment the preparation of the traffic information to be provided includes placing the transmission-relevant traffic data into a data format used aboard the vehicle, i.e. a data format that is used in the terminal aboard the vehicle, which receives and passes on traffic information after it is transmitted. As a result, existing vehicle terminals can be used practically unchanged for the present system according to the invention. If, for example, the vehicle terminal can process only traffic jam reports as traffic information, cost function values adapted by the center for the relevant route edges, to the extent that they correspond to a traffic state resembling a traffic jam, are processed into fictitious traffic jam reports and transmitted in this fashion.
As another feature, the traffic data preparation includes production of traffic events as individual traffic objects that are accordingly identifiable. Such events for example can be assigned to recognized special traffic flow condition such as traffic jams, slow traffic, etc. or to a detected excessive variation in the selected cost function value from a normally expected reference cost function, with the reference cost function value (for example, the cost function value that stands for undisturbed free traffic flow).
As another variation, the traffic data preparation includes generation of delete messages with which specifically the traffic information that was prepared at an earlier point in time can be marked as no longer valid and can be deleted. This prevents earlier traffic information, that is no longer valid because of the traffic situation having changed in the meantime, from being stored too long in the vehicle terminal and possibly distorting other traffic information that depends on it, so that a route that is not longer optimal could be calculated in the vehicle because the resultant cost function values would be incorrect.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.